Provide UnitThreatSituation API response without giving target

[dfherr]

provide a threatStatus response similar to the retail API https://wowwiki.fandom.com/wiki/API_UnitThreatSituation

This means threatStatus is determined by the highest status on any target.

This requires a loop over the targets of all party/raid members and their pets to determine if the provided unit is tanking (or in danger of tanking) in any of them.